Steam power plant with steam turbine unit and process steam consumer, and method for operating a steam power plant with steam turbine unit and process steam consumer

ABSTRACT

A steam power plant having at least one steam turbine unit and a process steam consumer is provided. The process steam consumer includes a heat exchanger. The steam turbine unit is connected to a heat exchanger by means of a extraction steam line, and a desuperheater is connected in the primary side of the extraction steam line, so that process steam extracted through the extraction steam line of the turbine system may be conditioned by the desuperheater to the process conditions of the process steam consumer, and the heat energy removed in the desuperheater can be fed back into the steam power plant system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2010/058517, filed Jun. 17, 2010 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 09165561. EP filed Jul. 15, 2009. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention refers to a steam power plant with steam turbine unit and process steam consumer, especially a separator for carbon dioxide as the process steam consumer. The invention also refers to a method for operating a steam power plant with a steam turbine unit and a process steam consumer.

BACKGROUND OF INVENTION

Steam power plants (SPP) for generating electric power essentially comprise a steam turbine unit and a fired boiler, or, in the configuration as a gas and steam turbine power plant (CCPP), comprise a gas turbine unit with downstream heat recovery steam generator and steam turbine unit. Steam or power for secondary processes, which are not directly associated with the electric power generation, are customarily extracted from power plants of these types at corresponding points. Thus, for example a flue gas scrubbing plant, for example a carbon dioxide separator, which is connected downstream to the power plant, is operated with process steam which is extracted from the steam turbine unit at an intermediate stage of the steam turbine unit.

A further example of process steam extraction from the steam turbine unit is district heating supply. The quantity of extracted steam in this case is dependent upon the mode of operation of the process steam consumer or of the separator for carbon dioxide. The extracted quantity of steam in this case leads to a reduction of the mass flow of steam which is absent from the following turbine stages of the steam turbine unit after the extraction. As a rule, process steam consumers, such as a carbon dioxide separator, require process steam at a corresponding pressure and temperature level.

For current concepts of separators for carbon dioxide, a large quantity of thermal energy is required, for the process steam has to be extracted from the water-steam cycle of the power plant. The thermal energy is introduced into the desorption unit of the separator for carbon dioxide as a result of condensation of the process steam. A minimum pressure, which lies between 2 and 4 bar, for the process steam results from this. At this pressure level, the steam in modern power plants with reheating and high steam temperatures, however, is more highly superheated. The energy of such highly superheated steam can be used only unsatisfactorily during normal heat transfer in heat exchangers.

Therefore, in known power plants the extracted process steam is reduced in temperature level, and consequently slightly superheated, by injecting water. In the case of the injected water, as a rule it is condensate from the water-steam cycle of the power plant. For the desorption process, no advantages emerge as a result. In particular, the energy which lies in the superheating of the steam not being optimally utilized is disadvantageous to this known method. Also, the extraction of condensate from the water-steam cycle of the power plant for injecting into the highly superheated steam as cooling medium is costly.

Flow losses, which arise because of high-quality process steam, for example highly superheated steam, being extracted from the steam turbine unit, are a general disadvantage to steam power plants with process steam consumers which are known from the prior art, although slightly superheated steam is sufficient for the process steam consumers.

SUMMARY OF INVENTION

It is therefore an object of the invention to propose a steam power plant with steam turbine unit and process steam consumer, in which the steam which is extracted from the turbine unit can be used in an energetically advantageous and largely comprehensive manner. It is a further object of the invention to propose a method for operating a steam power plant with steam turbine unit and process steam consumer, in which the process steam which is extracted from the steam power plant process is conditioned in an energetically advantageous manner for the process steam consumer.

The object of the invention which is focused upon a steam power plant is achieved with a steam power plant with at least one steam turbine unit and a process steam consumer, wherein the process steam consumer comprises a heat exchanger, and the steam turbine unit is connected via a bleed line to the heat exchanger, wherein a desuperheater is connected into the bleed line on the primary side.

The invention in this case is based on the idea of achieving a conditioning of a process steam, which is extracted from the steam turbine unit, for the process steam consumer by means of a desuperheater. By means of the desuperheater, it is possible to bring the process steam to a temperature level which is optimized for the process steam consumer. In this case, the desuperheater enables a further use of the energy which is extracted from the process steam. Desuperheaters of this type can be designed as heat exchangers, the desuperheater absorbing energy on the primary side and transferring it to a medium on the secondary side in the process. By using a desuperheater, moreover, other measures for adjustment of the temperature level, such as injecting water or condensate, can theoretically be dispensed with. The invention therefore enables use of the energy which is extracted by means of the desuperheater during simultaneous conditioning of the process steam for the downstream process steam consumer, as a result of which the overall efficiency of the steam power plant is appreciably increased. The invention can also be realized, moreover, with shorter piping routes compared with known interconnections, as a result of which costs for the steam power plant are reduced.

In an advantageous development of the steam power plant, the steam power plant furthermore comprises a water-steam cycle with a main condensate line and a return condensate line, wherein the desuperheater is connected into the return condensate line on the secondary side. This type of interconnection advantageously enables use of the energy which is drawn from the process steam by means of the desuperheater for preheating a condensate in the water-steam cycle of the steam power plant. As a result of the contribution of the desuperheater for preheating the condensate, a preheater for condensate preheating, which is connected downstream to the desuperheater on the secondary side, is unloaded. As a result, the bled steam from the steam turbine unit which is required for this preheater can be reduced, as a result of which the portion of operating steam in the steam turbine unit is increased. However, as a result of cooling the process steam in the desuperheater, a larger quantity of steam becomes necessary for feeding into the desuperheater in order to be able to provide the same amount of heat, in the form of process steam, for the process steam consumer. Therefore, by using the desuperheater, a shift of the steam quantities especially takes place, but since the bled steam which is at higher pressure, and therefore of higher quality, is reduced, an efficiency enhancement of the steam power plant results from this. By using the condensate as cooling medium for the desuperheater, a costly extraction of main condensate in the water-steam cycle as cooling medium can furthermore be avoided. As a result, the number of interfacing points is reduced and the process-engineering integration is simplified.

In a special development of the steam power plant, the process steam consumer is a separator for carbon dioxide from a flue gas. Carbon dioxide separators of this type require a large quantity of thermal energy which inevitably is extracted from the water-steam cycle of the steam turbine power plant in the form of process steam. The extracted process steam in this case is required particularly for the desorption or regeneration of a solvent. A process requirement of the flue gas scrubbing is a minimum temperature level, as a result of which, in the case of heat transfer by condensation according to current knowledge, a minimum pressure of the process steam of between 2 and 4 bar results. At this pressure level, the steam, during a normal power plant process with reheating and high steam temperatures, is still highly superheated. The energy of the superheated steam can be used only unsatisfactorily in a desorption process without upstream desuperheating since only the saturated steam level of the process steam is relevant for the transfer of heat.

The bleed line is advantageously connected to the crossover line of the steam turbine unit. The crossover line connects the intermediate-pressure turbine to the low-pressure turbine. An extraction of process steam at the crossover line is constructionally simpler to realize than the extraction of process steam between the stages of the steam turbines.

By means of the invention, it is possible to extract the steam which is required for a process steam consumer from a favorable point of the steam turbine unit, and to feed the steam to a process steam consumer in an energetically advantageous manner. A resulting superheated portion of the process steam can be advantageously used at another point of the steam power plant as a result of the desuperheater according to the invention.

The object of the invention which is focused upon a method is achieved by means of a steam power plant with a steam turbine unit and process steam consumer, wherein superheated steam is extracted from the steam turbine unit at a first process stage, and at a second process stage the superheated steam is desuperheated, wherein heat is extracted from the superheated steam and slightly superheated steam is formed, and wherein the slightly superheated steam is fed to the process steam consumer.

The invention is based in this case on the consideration of providing for the process steam consumer a conditioned steam, in the form of slightly superheated steam, which was previously extracted in a first process stage from the steam turbine unit in the form of superheated steam and which was desuperheated in a second process stage.

In an advantageous further development, the steam power plant furthermore comprises a water-steam cycle, wherein the heat which is extracted from the superheated steam is fed to the condensate of the water-steam cycle of the steam power plant. As a result, the energy which is drawn from the desuperheater can be used for preheating a condensate in the water-steam cycle of the steam power plant. As a result of the contribution of the desuperheater towards the preheating of the condensate, a preheater for condensate preheating, which is connected downstream to the desuperheater on the secondary side, is unloaded. The necessary bled steam from the steam turbine unit can be reduced for this preheater, as a result of which the portion of operating steam in the steam turbine unit is increased.

In a particular further development of the steam power plant process, the slightly superheated or conditioned steam is used in the process steam consumer for the separation of carbon dioxide. The conditioned steam in this case is used especially for the desorption or regeneration of a solvent.

The superheated steam is advantageously extracted from the steam turbine unit from the crossover line between the intermediate-pressure stage and the low-pressure stage. An extraction of the process steam at the crossover line is constructionally simpler to realize than the extraction of process steam between the stages of the steam turbines.

BRIEF DESCRIPTION OF THE DRAWINGS

The exemplary embodiments of the invention are subsequently explained in more detail with reference to an attached schematic drawing.

DETAILED DESCRIPTION OF INVENTION

The steam power plant 1 which is shown in FIG. 1 essentially shows a steam turbine unit 2 and a process steam consumer 3 and also a desuperheater 6.

The steam turbine unit 2 shows an intermediate-pressure turbine 9 and a low-pressure turbine 10, which are interconnected via a crossover line 11. During operation of the steam power plant 1, superheated steam leaving the intermediate-pressure turbine 9 can therefore be transferred into the low-pressure turbine 10. The bleed line 5 is connected to the crossover line 11. Some of the superheated steam can be branched off from the crossover line 11 through the bleed line 5.

The bleed line 5 is furthermore connected to the desuperheater 6 on the primary feed side. On the primary discharge side, the desuperheater 6 is connected to the process steam consumer 3. By means of the desuperheater 6, heat is extracted from superheated steam which is guided in the bleed line 5. Slightly superheated steam leaves the desuperheater on the primary discharge side.

The process steam consumer 3 in this case is shown only schematically. An essential interface point of the process steam consumer 3 with the steam turbine unit is especially a heat exchanger 4 which comprises the process steam consumer 3. The saturated steam, which is formed in the desuperheater 6 as a result of heat extraction, is fed to the heat exchanger 4 of the process steam consumer 3. In so doing, heat from the saturated steam is transferred to the process steam consumer, wherein the saturated steam condenses.

The return condensate from the process steam consumer 3 is now fed via the return condensate line 13 to the desuperheater 6 on the secondary feed side. In this case, the condensate is heated and discharged from the desuperheater 6 on the secondary side. The discharging in this case is carried out into the main condensate line 8 of the water-steam cycle 7 of the steam power plant 1. The condensate is provided for re-evaporation and reintroduction into the steam turbine unit 2.

As a result of heating the condensate from the process steam consumer 3 in the desuperheater 6, the preheater 12 a is unloaded. As a result of unloading the preheater 12 a, less steam has to be extracted from the steam turbine unit 2 for preheating the condensate. Consequently, the portion of operating steam in the steam turbine unit 2 is increased, from which results an efficiency enhancement of the steam power plant 1. 

1-8. (canceled)
 9. A steam power plant, comprising: a steam turbine unit; a desuperheater; and a process steam consumer, comprising: a heat exchanger, wherein the steam turbine unit is connected via a bleed line to the heat exchanger, and wherein the desuperheater is connected into the bleed line on the primary side.
 10. The steam power plant as claimed in claim 9, further comprising a water-steam cycle with a main condensate line and a return condensate line, and wherein the desuperheater is connected into the return condensate line on the secondary side.
 11. The steam power plant as claimed in claim 9, wherein the process steam consumer is a separator for carbon dioxide from a flue gas.
 12. The steam power plant as claimed in claim 9, wherein the steam turbine unit comprises a intermediate-pressure turbine and a low-pressure turbine, wherein the intermediate-pressure turbine is connected to the low-pressure turbine via a crossover line, and wherein the bleed line branches off from the crossover line.
 13. A method for operating a steam power plant with a steam turbine unit and a process steam consumer, comprising: extracting superheated steam from the steam turbine unit at a first process stage; desuperheating the superheated steam at a second process stage wherein heat is extracted from the superheated steam and slightly superheated steam is formed; and feeding the conditioned steam to the process steam consumer.
 14. The method as claimed in claim 13, wherein the steam power plant comprises a water-steam cycle and the heat which is extracted from the superheated steam is fed to the condensate of the water-steam cycle of the steam power plant.
 15. The method as claimed in claim 13, wherein in the process steam consumer the conditioned steam is used for a carbon dioxide separating process.
 16. The method as claimed in claim 13, wherein the superheated steam is extracted from the steam turbine unit from a crossover line between an intermediate-pressure stage and a low-pressure stage. 